Posited (Verb)-  to assume or affirm the existence of.
The content in which the word was used is, “a 2015 thesis by Rose K. Pozos about the “urban sociability” of coffee shops posited that sitting alone with a laptop in a café was not nnecessarily antisocial.”
Article: Coffee Shop Skip Wi-Fi to Encourage Customers to Actually Talk.
Therefore, she is saying that coffee shops assume sitting unaccompanied with a laptop in a café is not necessarily antisocial.